Fluid pressure regulators regulate the flow of fluid between a high pressure port and a low pressure port. Typically, regulators are preset to allow fluid to flow when pressure at a low pressure port drops below a predetermined upper limit.
One type of pre-set regulator is known as a piston-type regulator. This regulator typically comprises a valve body, a hollow stem piston and a spring. When fluid pressure at the low pressure port of the valve body drops below a pre-set minimum, a coil spring operating on the underside of the piston head lifts the piston operated stem valve off the high pressure inlet port to provide fluid flow between the inlet port and the outlet port. At the same time, some of the fluids flow up the hollow piston stem to be captured in the cylinder head between the head of the valve body and piston face. As pressure at the outlet port increases, so does back pressure in the cylinder forcing the piston down and the piston stem valve against the high pressure inlet port.
U.S. Pat. No. 4,924,904 discloses a piston-type pressure regulator having a variable pressure differential adjustability through the use of a camming plate that can adjustably preload the spring which acts on the piston body, tending to force the stem of the piston off the high-pressure valve seat. This is effected by adjusting the preload on the spring against the piston and selectively compressing the spring to achieve the desired pressure differential (cut-off pressure) of the piston stem against the valve seat.
Applicant's invention provides, however, in a unique piston type fluid regulator, the capability of providing in a single regulator a device capable of adjustably selecting a cut-off pressure.